Method and apparatus for dissolved air flotation with aeration

ABSTRACT

A method and apparatus for aeration of waste water in a dissolved air flotation waste water treatment system includes a container for receiving and retaining waste water for settling of heavy particles and flotation of light particles to the surface of the waste water. Waste water is removed from the container and supplied to a free standing tank. Pressure in the tank is maintained at a predetermined level through the injection of compressed air into the tank. Waste water removed from the tank is pumped through a multiple jet configuration wherein air from the tank is entrained in the waste water as the water is injected back into the tank. The aerated water is discharged from the tank back into the container, thereby providing an efficient aeration process. Aerating the water in a free standing tank separate from the container increases clarification quality as a result of reduced disturbance of the particles floated to the surface of the waste water and reduced need for chemical addition to the waste water.

TECHNICAL FIELD The present invention relates generally to dissolved airflotation treatment of waste water, and more particularly to a dissolvedair flotation system having an aeration system separate from thedissolved air flotation ("DAF") container. BACKGROUND OF THE INVENTION

In the treatment of waste water in a dissolved air flotation ("DAF")system, the solids are clarified through means of flotation of particlesto the surface of the liquid. The flotation of particles to the surfaceof the liquid has been accomplished in the past through various means ofaerating the waste water.

In a typical dissolved air flotation system, recycled water or the rawwaste water is pressurized. Compressed air is added to thepressurization tank. This water, along with flocculating chemicals isintroduced into the DAF vessel. Bubbles are formed as the air entrainedin the water is released from pressure. The particles attach themselvesto or become trapped by the bubbles. As the bubbles rise to the surfaceof the water, the particles are carried along. When the bubbles reachthe surface the air escapes, forming a foam or sludge layer on thesurface. The sludge layer contains the particles deposited by theescaping air bubbles. The sludge layer is kept intact and skimmed fromthe vessel to be processed by various means. Thus, through aeration, thewaste water is fed needed air and chemicals and the water clarified.

Presently available methods and apparatus for aerating waste water in aDAF treatment system have failed to efficiently entrain sufficientamounts of air in the waste water necessary to obtain maximum particleflotation without substantial use of chemicals. Additionally, aerationof waste water using prior art methods and apparatus has furtherresulted in excess movement or circulation of the treated waste water,damaging the sludge layer formed.

SUMMARY OF THE INVENTION

The present invention overcomes the above difficulties by recirculatingwaste water from the dissolved air flotation ("DAF") container throughan aeration system of the present invention for aeration of the wastewater with minimum disturbance of the interior area of the DAFcontainer. Aeration in a system remote from the DAF container maximizesair entrainment in the waste water before returning the water to the DAFcontainer and thereby minimizes the need for flocculating chemicals.Thus, cycling of the water from the DAF container through the aerationsystem and back into the DAF container results in improved airentrainment in the water to increase flotation of particles, moreefficient air utilization, and further clarification of the waste waterwith substantially less or no chemical addition, thereby creating a moreefficient means of treating the waste water, increasing the quality ofthe resulting effluent, and producing a more easily handled sludgelayer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be had by referenceto the following Detailed Description when taken in conjunction with theAccompanying Drawings wherein:

FIG. 1 is a perspective view of a dissolved air flotation system havinga DAF container and an aeration system through which the waste water isrecycled in accordance with the invention;

FIG. 2 is a side view of the DAF container of FIGURE 1;

FIG. 3 is a top view of the DAF container of FIGURE 2;

FIG. 4 is a front view of the DAF container of FIGURE 2, illustrating ingreater detail the outlets through which the waste water is cycled tothe aeration system;

FIG. 5 is a back view of the DAF container of FIGURE 2, illustrating ingreater detail the inlets for returning aerated water from the aerationsystem to the DAF container; FIG. 6 is a side view of the recycle pumpand pipe configuration for directing waste water from the DAF containerto the aeration system of FIG. 1;

FIG. 7 is a top view of the recycle pump and pipe configuration of FIG.6;

FIG. 8 is a side view of the aeration system of FIG. 1;

FIG. 9 is a top view of the aeration system of FIG. 8;

FIG. 10 is a partial top view similar to FIG. 9 showing only the air andwater jet configuration of the aeration system of FIG. 8;

FIG. 11 is a side view of the piping configuraiton for directing theflow of aerated water from the aeration system of FIG. 8 to the DAFcontainer of FIG. 2; and

FIG. 12 is a top view of the piping configuration of FIG. 11.

DETAILED DESCRIPTION

Referring now to the Drawings, and more particularly to FIG. 1, there isshown a dissolved air flotation system 10 incorporating the presentinvention. The dissolved air flotation system 10 includes a dissolvedair flotation ("DAF") container 12 having sides 12a and 12b, a front12c, and a back 12d. Waste water in the container 12 is pumped by arecycle pump 14 from an outlet 16 in the uppermost end of the DAFcontainer 12 near the front 12a through a recycle pipe 18. A motor 20supplies operating power to the pump 14 to direct the flow of wastewater through connecting pipe 22 to an aeration tank 24 as part of theaeration system 25.

A motor 28 provides operating power to an aeration pump 30 to pump wastewater from the aeration tank 24 into a plurality of jets 26. Compressedair from the top of the aeration tank 24 passes through a pipingconfiguration 32 into the jets 26 where it is entrained in the wastewater as the water is forced through the jets by the pump 30 as a highpressure stream. The aerated water is then forced under pressure backinto the aeration tank 24.

The aerated water in the aeration tank 24 is continuously returned tothe DAF container 12 through a return piping configuration 34. Airpressure in the aeration tank 24 is maintained between 80 and 100 psi bymeans of a compressed air source (not shown) connected to the aerationtank through a compressed air inlet 35. The aerated water flows from theaeration tank 24 through the return piping 34 as a result of themaintained tank pressure. Return piping 34 intersects with a surge tankpipe 36, mixing the aerated water from the return piping with raw sewagein the surge tank pipe and channeling the resulting mixture throughinlet 38 into the lowermost part of the back 12d of the DAF container12.

The aeration cycle is a continuous one whereby approximately one-third(1/3) to one-half (1/2) of the total flow through the dissolved airflotation system 10 is passed through the aeration tank 24, therebyincreasing the level of aeration of the system to improve flotation ofparticles from the water, and resulting in higher levels of clarity ofthe treated waste water.

Referring now to FIGS. 2, 3, 4 and 5 there is shown the DAF container 12of FIG. 1. Raw waste water sewage is introduced into the DAF container12 from inlet 38 through inlet pipe 40. The raw waste water sewage thenenters a chamber 42 from where it flows into the DAF container 12. TheDAF container 12 is supported on legs 50 equally spaced along the lengththereof. Heavy particles contained in the raw waste water settle to thebottom of the DAF container 12. Lighter particles are floated to thesurface of the water by air bubbles contained within the water in thecontainer 12. As the particles are floated to the surface of the liquidheld in the container 12, a foam or sludge layer forms on the top of theliquid.

A rake 52 having paddles 54 mounted on chains 56 skims the foam layerfrom the liquid, into a discharge chute 58 and out through a drain 60 asthe chains are moved by means of rotating sprockets 62. The rake 52passes over a frame 64 mounted above and to the walls of the container12 as the chains 56 rotate with the sprockets 62.

Waste water having the desired degree of clarification is dischargedfrom the container 12 into an effluent discharge chute 66 and out adrain 68 after passing under a baffle 63 and over a dam 65 as shown inFIGS. 2, 3, and 4. The heavier particles that settle to the bottom ofthe container 12 are discharged from the system through drains 70 into adrain pipe 72, and out through outlets 74 as shown in FIGS. 2, 3, and 5.

Referring now to FIGS. 2, 3, 4, 6, and 7, to increase the number of airbubbles in the water and thereby improve flotation of the lighterparticles to the surface, the water is withdrawn from the container 12through drains 46 into an outlet pipe 48 from where it is pumped throughthe particular outlet 16 having the recycle pipe 18 connected thereto.The flow of the water from the container 12 is directed through therecycle pipe 18 into the aeration system 25.

Referring now to FIGS. 6 and 7, the waste water circulated from the DAFcontainer through the aeration system is pumped from the DAF container12 and into the recycle pipe 18 by the recycle pump 14. The recycle pump14 is preferably of the type manufactured by Crane-Deming and sold asModel No. 4021. The pump 14 is driven by a motor 20 and pumps wastewater from the DAF container 12 through the recycle pipe 18, through aconcentric reducer 76 into the aeration tank 24. As shown in FIG. 7, afull port ball valve 78 regulates the flow of water from the recyclepipe 18 and into the pump 14. The recycle pump 14 and motor 20 aremounted on a base 80 mounted on pump mount runners 82 as shown in FIGS.2 and 3. As shown in FIGURE 6, a full port ball valve 86 directs wastewater from the recycle pipe 18 in the event of maintenance and repairs.The flow of waste water from the recycle pump 14 passes through and iscontrolled by a check valve 88 and a full port ball valve 90. The wastewater then passes through a concentric expander 92 into the connectingpipe 22 for delivery to the aeration tank 24.

Referring now to FIG. 8, as the waste water is delivered through theconnecting pipe 22 to the aeration tank 24 it passes through aconcentric expander 100 into a delivery pipe 102. The waste water in thedelivery pipe 102 then passes through an inlet 104 in the top center ofthe aeration tank 24.

As shown in FIGS. 8 and 9, compressed air is input into the aerationtank 24 through a pipe 106 and a check valve 110, with the flow ofcompressed air being controlled by a solenoid valve 108. The compressedair supply piping also includes a reducer tee 112 connected to an inletpipe 114 mounted in the top of the aeration tank 24. The pressure in theaeration tank 24 is maintained at 80-100 psi with the result that thewaste water is maintained at a level of approximately 36", indicated byline 116, to provide continuous flow of aerated water from the systemwhile achieving maximum entrainment of air in the water.

A visual level indicator 118 continuously indicates and controls thelevel of the waste water in the aeration tank 24. The level indicator118 is preferably of the type manufactured by Granzow, Inc. and soldunder Model No. BMG-1''150RF-VKM60"-MNA. The level indicator 118 isconnected to the interior of the aeration tank 24 at one point by aconnecting pipe 120 positioned in the wall of the tank 24 at a pointwell below the water level 116. A pipe 122 connects the level indicator118 to the aeration tank 24 at a second point well above the water level116.

Compressed air in the upper portion of the aeration tank 24 enters thelevel indicator 118 through the pipe 122. Waste water from the aerationtank 24 is forced under the action of the maintained pressure into thelower portion to the level indicator 118 through the connecting pipe120.

Located in the level indicator 118 are two magnetic switches (not shown)connected through a conventional electrical system (not shown) to thesolenoid valve 108. As the water in the level indicator 118 contacts theuppermost switch, the solenoid valve 108 is opened to allow the flow ofcompressed air into the aeration tank 24, thereby lowering the waterlevel. As the water level drops below the lowermost magnetic switch, thesolenoid valve 108 is closed to halt the flow of compressed air into theaeration tank 24, allowing the water level in the tank to rise. Thus,the water level in the aeration tank 24 is continuously measured andcontrolled by the level indicator 118.

A drain pipe 124 and a ball valve 126 are connected to the wall of theaeration tank 24 to allow for draining of waste water from the aerationtank.

Referring now to FIGS. 8 and 9, the water in the aeration tank 24 isaerated by pumping the water from the aeration tank through an outletpipe 130 by means of the aeration pump 30. The aeration pump ispreferably of the type manufactured by Crane-Deming and sold under ModelNo. 4011. Operative power for the aeration pump 30 is provided by themotor 28. The motor 28 and aeration pump 30 are mounted on a channelbase 140 having angle clip feet 142.

Referring now to FIGS. 8, 9, and 10, a full port ball valve 134connected in the outlet pipe 130 provides a means for draining the wastewater from the aeration pump 30 and aeration tank 24. The waste waterfrom the aeration tank 24 is pumped by means of the aeration pump 30into a manifold 136 mounted above the aeration pump and parallel to theaeration tank. The waste water in the manifold 136 is pumped underpressure through a multiple unit jet configuration 26 wherein each unitcomprises a coupling 146 attached to the manifold 136 at one end and anipple 148 on the other end. Mounted to the nipple 148 is a ball valve150 which regulates the flow of waste water from the manifold 136 into ajet 152, preferably of the type manufactured by Penberthy and sold bythat company under Model No. M-1-575. The ball valve 150 is connected bya nipple 154 to a female union 156, in turn connected to an elbow 158 bya nipple 160. The elbow 158 is connected by a nipple 162 to a threadreducer coupling 164, in turn connected to the jet 152 by a nipple 166.The water is forced under pressure through the piping configuration andinto the jet 152 as a high pressure stream.

Still referring to FIGS. 8, 9, and 10, compressed air from thecompressed air contained in the upper portion of the aeration tank 24 isalso introduced into the jets 152. The compressed air from the aerationtank 24 passes through a pipe 168 mounted in the top of the aerationtank 24 and extending downwardly for attachment to the top of an airmanifold 170. The air is directed from the air manifold 170 into thejets 152 through a multiple pipe configuration similar to the pipeconfiguration directing the flow of waste water from the manifold 136 tothe jets 152. Thus, as shown in FIGS. 9 and 10, for each pipingconfiguration, there is attached to the air manifold a coupling 172connected by a nipple 174 to a full port ball valve 176, to regulate theflow of the compressed air into the jet 152. The ball valve 176 isconnected by a nipple 178 to a female union 180, in turn connected by anipple 182 to the jet 152.

As the compressed air enters the jets 152, it is entrained into the highpressure stream of water being forced through the jets 152, therebymixing the compressed air and waste water under pressure and forcing theresulting aerated water back into the aeration tank 24 through a fullport ball valve 184. The valve 184 regulates the flow of the highpressure stream of aerated water from the jets 152 into the aerationtank 24 and is connected to the aeration tank 24 through a nipple 186connected to a coupling 188 mounted to the wall of the aeration tank 24at a point well below the water level 116. By means of a nipple 190, theball valve 184 is connected to a male/female union 192, in turnconnected to the discharge section 194 of the jet 152. The action ofpumping the waste water through the multiple jet configuration 26efficiently utilizes the compressed air to more completely aerate thewaste water than existing prior art apparatus.

Still referring to FIGS. 8 and 9, there is located in the top of theaeration tank 24 a sample outlet 196 for checking the contents of theaeration tank 24 and a safety/relief valve 198 to allow for the releaseof excess pressure in the aeration tank 24. As the waste water iscontinually recycled and aerated through the multiple jet configuration26, aerated waste water is also being returned from the aeration tank 24to the DAF container 12. The aerated water exits the aeration tank 24through a pipe 200 having a flange 202 and a concentric reducer 204 fordirecting the aerated water through the pipe 34 into the DAF container12.

Referring now to FIGS. 11 and 12, the flow of aerated waste water in thepipe 34 to the DAF container 12 is regulated by a globe valve 220. Asthe aerated water passes through the globe valve 220, it makes a 45°turn through an elbow 222 and enters the surge tank pipe 36. The surgetank pipe 36 is connected at the uppermost end through a concentricreducer 226 to a pipe 228 from a waste water surge tank (not shown).Thus, the surge tank pipe 36 receives aerated water from the aerationtank 24 as well as raw sewage from the surge tank. As shown in FIGS. 1and 11, the surge tank pipe 36 is connected to the DAF container 12 byan elbow 230 attached to an inlet 38.

Again referring to FIGS. 1, 2, 3 and 5, as the aerated waste waterpasses through the inlet 38, it enters the inlet pipe 40 and moves intothe chamber 42 from where it ultimately flows into the DAF container 12.After the aerated waste water enters the DAF container, particlesentrained by the bubbles are floated to the surface of the waste waterbeing held in the DAF container 12 to further clarify the waste water.

By aerating the waste water through use of the above-described methodand apparatus, the compressed air is more efficiently utilized to obtaingreater aeration of the waste water with a resultant increase inclarification. Additionally, the method of aerating the waste wateroutside of the DAF container 12 results in less movement in the DAFcontainer contents, thereby reducing the disturbance of the sludgelayer, and allowing for more efficient flotation of lighter particles tothe surface of the waste water contained within the DAF container.

Although the preferred embodiment of the present invention has beenillustrated in the accompanying Drawings and described in the foregoingDetailed Description, it will be appreciated by those skilled in the artthat various modifications and rearrangements of the component parts andelements of the present invention are possible within the scope of thepresent invention.

We claim:
 1. Apparatus for aerating water in a dissolved air flotation system comprising:pressure tank means having a pressurized air inlet means connected to an upper portion of said pressure tank means to pressurize said pressurized tank means to a predetermined pressure; said pressure tank means having inlet means for receiving water to be aerated; control means for maintaining the water level in the pressurized tank means at a predetermined level, said control means comprising a water level sensign means operatively connected between said pressure tank means and means for regulating the flow of pressurized air through said pressurized air inlet means; aeration means connected to receive water from said pressure tank means for aeration of the water, comprising:a plurality of jets for entraining air in the water as the water is forced through the jets back into the pressure tank means; pump means; a water manifold connected to the pump means; connecting means separately connecting each of the jets to the water manifold; an air manifold; means connecting the air manifold to the pressure tank means; connecting means separately connecting each of the jets to the air manifold; means for connecting water from the pressure tank means to the aeration means; and means for returning the aerated water back to said pressure tank means.
 2. The apparatus of claim 1 wherein said pressurized air inlet means further maintains a substantially constant pressure in the pressure tank means.
 3. The apparatus of claim 1, wherein said control means comprises a pair of magnetic switches.
 4. Apparatus for aerating water in a dissolved air flotation system, comprising:flotation container means for receiving waste water and for receiving and retaining aerated waste water to allow flotation of particles to the surface of the waste water held therein; means for supplying waste water to the flotation container means; pressure tank means pressurized to a predetermined pressure connected to receive waste water from said flotation container means; means for pumping waste water from said flotation container means into said pressure tank means; means for pressurizing said pressure tank means; aeration means connected to receive waste water from said pressure tank means; said aeration means comprising: a plurality of jets for entraining air in the waste water as the waste water is forced through the jets; a water manifold for connecting the waste water from the pressure tank means to the jets; an air manifold for connecting pressurized air from the pressure tank means to the jets; connecting means separately connecting each of the jets to the air manifold; connecting means separately connecting each of the jets to the water manifold; and means connecting each of the jets to the pressure tank means means for returning the aerated waste water from the pressure tank means to the flotation container means.
 5. The apparatus of claim 4 wherein the means for pumping waste water from the flotation container means into the pressure tank means comprises pump means and means connecting the pump means to the container and to the pressure tank means.
 6. The apparatus of claim 4, including means for maintaining a substantially constant pressure in the pressure tank means.
 7. The apparatus of claim 7 wherein said means connecting the jets to the air manifold includes a valve for regulating the flow of pressurized air from the manifold into the jets.
 8. The apparatus of claim 4, wherein said means connecting the jets to the pressure tank means includes a valve for regulating the flow of aerated waste water from the jets into the pressure tank means.
 9. The apparatus of claim 4 further comprising pump means connecting the pressure tank means to the water manifold.
 10. The apparatus of claim 4 wherein the means for returning the aerated waste water from the pressure tank means to the flotation container means connects to the pressure tank means at a location below the water level and empties the waste water into the flotation container means at substantially the lowermost location in the flotation container means.
 11. The apparatus of claim 4, comprising level indicator means connected to the pressure tank means for continuous monitoring and control of the level of waste water in the pressure tank means.
 12. Apparatus for aerating water in a dissolved air flotation system, comprising:flotation container means for receiving water and for receiving and retaining aerated water to allow flotation of particles to the surface of the water held therein; means for feeding water to the flotation container means; pressure tank means pressurized to a predetermined pressure connected to receive water from said flotation container means; means for pumping water from said flotation container means into said pressure tank means; means for pressurizing said pressure tank means; aeration means connected to receive water from said pressure tank means for aeration of the water, comprising:a plurality of jets for entraining air in the water as the water is forced through the jets; a water manifold for connecting water from the pressure tank means to the jets; an air manifold for connecting pressurized air from the pressure tank means to the jets; means for separately connecting each of the jets to the water manifold; means for separately connecting each of the jets to the air manifold; and means connecting each of the jets to the pressure tank means; means connecting the air manifold to pressurized ai contained in the pressure tank means; means for connecting water from said pressure tank means to said water manifold; and means for returning the aerated water from the pressure tank means to the flotation container means.
 13. The apapratus of claim 12 wherein the means for pumping water from the flotation container means into the pressure tank means connects to the container below the normal water surface.
 14. The apapratus of claim 12 including means for maintaining a substantially constant pressure in the pressure tank means.
 15. The apapratus of claim 12, wherein said means for connecting the jets to the air manifold includes a valve for regulating the flow of pressurized air from the manifold into the jets.
 16. The apapratus of claim 12, wherein said means for connecting the jets to the pressure tank means includes a valve for regulating the flow of aerated water from the jets into the pressure tank means.
 17. The apapratus of claim 12 wherein the means for connecting water from the pressure tank means to the water manifold comprises pump means.
 18. The apapratus of claim 12 wherein the means for returning the aerated water from the pressure tank means to the flotation container means returns the water to the flotation container means at substantially the lowermost location in the flotation container means.
 19. The apparatus of claim 12, further comprsiing a level indicator means connected to the pressure tank means for continuous monitoring and control of the level of water in the pressure tank means. 